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Chemical Analysis using paper chromatography

Chemical Analysis using paper chromatography

Artificial colouring may be separated by chromatography

  • Food colouring may contain one dye or a mixture of dyes
  • You place the food colouring (a few drops) in small cup with a few drops of solvent (water, ethanol etc.)
  • Put spots of the coloured solution
  • Get a piece of filter paper and draw a line on it – put spots of the coloured solution on the base line
  • Roll up the filter paper and in a new beaker of solvent – make sure the solvent is below the base line
  • The solvent will go up the filter paper and the colours will separate and stop at a different position on the filter paper
  • g. if you have three spots then you would have at least three different colours in the dye
  • This is used in industry all the time to analyse the content of substances – if you get the right mixture of solvent and dye then you very accurately separate different substances
  • Machines now do this much more accurately – advantages are that they are fast, accurate, sensitive to the tiniest amounts of changes

Gas chromatography

  • A gas is used to carry substances through a column packed with a solid material
  • The substances travel through at different speeds – so they are separated
  • The time taken to reach the other end is called a retention time
  • It draws a graph called the gas chromatograph
    • The number of peaks (called the molecular ion peak) shows the number of different compounds
    • The time shown between the peaks shows the retention time
  • The gas separates the substance and the gas spectrometer reads of their molecular mass – this means you can tell what the substance is
  • The gas spectrometer shows you how much of the substance was in the original substance and tells you the molecular mass of each part of the substance – then you can work out the weighted mass
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